Expr: Left([dob],4) = omitted an operator?

From: Jan (janoleolsen_at_hotmail.com)
Date: 05/30/04 

Date: Sun, 30 May 2004 19:55:22 +0200

Getting error saying "omitted an operator" when trying a simple function.
All I'm trying to do is get a list of the first 4 characters of a text field
of 6 characters.

Expr: Left([dob],4)